The present invention relates generally to systems for estimating turbocharger operating parameters, and more specifically to systems for estimating absolute boost pressure in a turbocharged internal combustion engine.
Turbochargers are well known devices for pressurizing intake air entering the combustion chambers of an internal combustion engine to thereby increase the efficiency and power output of the engine. In general, pressurizing the intake air increases the quantity of air entering the engine cylinders during the intake stroke, and this allows more fuel to be utilized in establishing a desired air-to-fuel ratio. Increased available engine output torque and power is thereby realized.
In a turbocharged engine, the exhaust manifold of the engine is fluidly coupled to a turbine component of the turbocharger via an exhaust conduit, and the exhaust gas flowing through the exhaust conduit causes a turbine wheel within the turbine to rotate at a rate determined by the pressure and flow rate of exhaust gas. A compressor wheel within a compressor component of the turbocharger is mechanically coupled to the turbine wheel, and is therefore rotatably driven by the turbine wheel. An inlet of the compressor receives fresh ambient air, and an outlet of the compressor is fluidly coupled to the intake manifold of the engine via an intake conduit. The rotatably driven action of the compressor wheel increases the amount of intake air supplied to the intake conduit, thereby resulting in an increased, or so-called xe2x80x9cboostxe2x80x9d, pressure therein.
An exhaust gas recirculation (EGR) system implemented in such a turbocharged engine supplies controlled amounts of exhaust gas from the exhaust manifold to the intake manifold via an EGR conduit. In order to sustain positive EGR flow through the EGR conduit, it is necessary to maintain the pressure in the exhaust conduit greater than that in the intake conduit, and turbochargers in EGR-based engines must therefore typically operate at higher rotational speeds than in non EGR-based engines. In either case, however, it is desirable to have accurate knowledge of the absolute xe2x80x9cboostxe2x80x9d pressure within the intake manifold at all times so that the turbocharger speed may then be controlled to ensure positive EGR flow while maintaining turbocharger speed within safe operating limits.
In cases where implementation of an absolute boost pressure sensor is impractical or cost prohibitive, and/or in cases where redundant absolute boost pressure information is desired, what is needed is a system for accurately estimating absolute boost pressure.
The present invention accordingly provides a system for estimating absolute boost pressure as a function of the temperature and pressure of air entering the turbocharger compressor, the rotational speed of the turbocharger and the rotational speed of the engine.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiment.